1. Field of the Invention
The invention relates to a variable speed transmission device, and more particularly to a transmission device capable of changing speed with stored energy.
2. Description of the Related Art
Conventional speed-changing devices usually shift a relative position between some gears in a gear set with the extra manpower or motor power so as to produce different engagement conditions and transmission paths and thus to achieve the object of changing the gear ratio.
Taiwan Patent Publication No. 541828 and U.S. Pat. Nos. 6,189,395; 6,244,124; 6,626,057; and 6,366,343, which respectively correspond to Taiwan Patent Publication Nos. 421401; 426290; 462568; and 476213 have disclosed speed-changing mechanisms for scanners in order to provide required speeds for the scanners to perform a high-resolution scanning process and a low-resolution scanning process. However, these prior arts still have to change the speed with the extra motor power. A motor control circuit for an additional motor has to be provided in order to provide the power for changing the speed. Thus, the apparatus cost is increased, a relatively large space is occupied, and the power-saving requirement cannot be satisfied because the extra power has to be consumed.
Therefore, it is an important object of the invention to provide a transmission device capable of changing speed without an extra motor power source.